Alban Hills Research Articles

Recurrence of volcanic activity along the Roman Comagmatic Province (Tyrrhenian margin of Italy) and its tectonic significance

The Roman Comagmatic Province (RCP) developed along the NW‐SE striking extensional Tyrrhenian margin of Italy since middle Pleistocene and includes ultrapotassic small eruptive centers and large volcanic districts. By means of a review and statistical analysis of a large data set of radiometric ages we demonstrate that in the RCP, major eruptive cycles occurred at different volcanic districts almost simultaneously and with an almost constant recurrence time. Our analysis started with the Alban Hills Volcanic District, where a detailed 40Ar/39Ar chronology of the eruptive cycles has been recently achieved, and then extended to include a database of 264 radiometric ages of the RCP volcanics published since 1980. Statistical treatment of the data set shows a marked non‐Poissonian behavior of volcanic activity through the whole magmatic province, with climax of each major eruptive cycle occurring simultaneously at the different districts approximately every 48 kyr. The concomitant eruption of many volcanic districts spreading over a 250‐km‐long chain implies a control mechanism acting at a regional scale. After discussing the possible relationship between tectonics, sea level changes, and volcanic activity we hypothesize that constant rates of slab retreat during middle Pleistocene could have been a key factor controlling the rate of magma upwelling and the major cycles of recharge of the magma chambers. As a working hypothesis, we propose that the duration of the cycles may be related to (1) progressive weakening of the crust due to magma underplating or (2) cyclic injection of convective plumes into the mantle wedge.

Coupling between earthquake swarms and volcanic unrest at the Alban Hills Volcano (central Italy) modeled through elastic stress transfer

We study a seismic swarm that occurred in 1989–1990 at the Alban Hills volcano and interpret the seismicity pattern in terms of Coulomb stress changes caused by magma intrusion in a local volcanic source and the extensional tectonic stress field. We first image the three‐dimensional (3‐D) structure of the volcano through a tomographic inversion of P waves and S‐P arrival times recorded by a temporary local network. A high Vp and Vp/Vs body exists beneath the area of most recent volcanic activity, which we interpret as a solidified magma body delimiting the position of the volcanic source. We have relocated 661 events (M ≤ 4.0) using this 3‐D velocity model and we have computed 64 fault plane solutions. Elevation changes, measured between 1951 and 1994 along a 33‐km‐long line crossing the western part of the volcano, reveal an uplift of 0.3 m. We model these data to constrain the position and geometry of the volcanic source. We compute the vertical deformation in a homogeneous half‐space, testing different volcanic sources (spherical magma chamber, sill and dike). We model the Coulomb stress changes caused by the local volcanic source and the regional tectonic stress field. The inflation of magma generates an increase of Coulomb stress larger than 0.5 MPa in the area where the seismicity is located. More than 85% of fault plane solutions are consistent with the stress perturbations induced by the volcanic source. We conclude that microearthquakes at the Alban Hills are promoted by elastic stress changes caused by volcanic unrest episodes.

Tephrochronology and tephrostratigraphy of two Pleistocene continental fossiliferous successions from central Italy

AbstractThe stratigraphical context of two Middle Pleistocene fossiliferous palaeosols from Central Italy (Abruzzo and Tuscany) have been studied. Small mammals and molluscs occur in both palaeosols, which are covered by tephra layers that were analysed using an interdisciplinary approach. Application of fission‐track dating to apatites separated from the Case Picconetto tephra (Pescara, Abruzzo), yielded an age of 0.48 ± 0.04 Ma, indistinguishable from those previously determined for the Campani Quarry (Lower Valdarno, Tuscany) (0.46 ± 0.05 Ma and 0.48 ± 0.05 Ma). Geochemical and petrographic investigations indicate that these tephra originated from different volcanoes, the Alban Hills Volcanic Complex and the Vico Volcano (Latium) respectively. Small mammal and mollusc assemblages indicate different palaeoclimatic and palaeoenvironmental conditions for the Case Picconetto and Campani Quarry palaeosols. Warm and humid conditions can be inferred for the Campani Quarry site, whereas open and cold conditions can be inferred for Case Picconetto. On the basis of faunal data, fission‐track dates and attribution of tephra to specific volcanic eruptions, we suggest a correlation of these faunas with marine oxygen isotope stage 14 (Case Picconetto) and with marine oxygen isotope stage 11 (Campani Quarry), respectively. Copyright © 2003 John Wiley & Sons, Ltd.

Post-caldera activity in the Alban Hills volcanic district (Italy): 40Ar/39Ar geochronology and insights into magma evolution

We present 24 40Ar/39Ar ages for the youngest volcanic products from the Alban Hills volcanic district (Rome). Combined with petrological data on these products, we have attempted to define the chronology of the most recent phase of activity and to investigate the magma evolution of this volcanic district. The early, mainly explosive activity of the Alban Hills spanned the interval from 561±1 to 351±3 ka. After approximately 50-kyr of dormancy, a mainly effusive phase of activity took place, accompanied by the strombolian activity of a small central edifice (Monte delle Faete). This second phase of activity spanned the interval 308±2 to 250±1 ka. After another dormancy period of approximately 50-kyr, a new, hydromagmatic phase of activity started at 200 ka at several centers located to the southwest of the Monte delle Faete edifice. After an initial recurrence period of approximately 50-kyr, which also characterized this new phase of activity, the longest dormancy period (approximately 80-kyr) in the history of the volcanic district preceded the start of the activity of the Albano and Giuturna centers at 70±1 ka. Results of our study suggest a quasi-continuous magmatic activity feeding hydromagmatic centers with a new acme of volcanism since around 70 ka. Based on data presented in this paper, we argue that the Alban Hills should not be considered an extinct volcanic district and a detailed re-assessment of the volcanic hazard for the area of Rome is in order.

Carbon dioxide and radon gas hazard in the Alban Hills area (central Italy)

The sudden and catastrophic, or slow and continuous, release at surface of naturally occurring toxic gases like CO 2, H 2S and Rn poses a serious health risk to people living in geologically active regions. In general this problem receives little attention from local governments, although public concern is raised periodically when anomalous toxic-gas concentrations suddenly kill humans or livestock. For example, elevated CO 2 concentrations have been linked to the death of at least 10 people in the central Italian region of Lazio over the last 20 years, while it was the CO 2 asphyxiation of 30 cows in a heavily populated area near Rome in 1999 which prompted the present soil-gas study into the distribution of the local health risk. A detailed geochemical survey was carried out in an area of about 4 km 2 in the Ciampino and Marino districts, whereby a total of 274 soil-gas samples were collected and analysed for more than 10 major and trace gas species. Data were then processed using both statistical and geostatistical methods, and the resulting maps were examined in order to highlight areas of elevated risk. General trends of elevated CO 2 and Rn concentrations imply the presence of preferential pathways (i.e. faults and fractures) along which deep gases are able to migrate towards the surface. The CO 2 and Rn anomalous trends often correspond to and are usually elongated parallel to the Apennine mountain range, the controlling structural feature in central Italy. Because of this fundamental anisotropy in the factors controlling the soil-gas distribution, it was found that a geostatistical approach using variogram analysis allowed for a better interpretation of the data. With regard to the health risk to local inhabitants, it was found that although some high risk areas had been zoned as parkland, others had been heavily developed for residential purposes. For example, many new houses were found to have been built on ground which has soil-gas CO 2 concentrations of more than 70% and radon values of more than 250 kBq m −3. It is recommended that land-use planners incorporate soil-gas and/or gas flux measurements in environmental assessments in areas of possible risk (i.e. volcanic or structurally active areas).

Short- and long-term gas hazard: the release of toxic gases in the Alban Hills volcanic area (central Italy)

In the Alban Hills area, strong areally diffuse and localised spot degassing processes occur (Tivoli, Cava dei Selci, Solforata, Tor Caldara). The gas comprises a large proportion of CO 2, with minor CH 4, H 2S and Rn. These advective features are generated by fluid leakage from buried reservoirs hosted in the structural highs of the Mesozoic carbonate basement. Gas migration towards the surface is controlled by fault and fracture systems bordering the structural highs of the carbonate formations (e.g. Ciampino high). His release is triggered when the total pressure of the fluid phase exceeds the hydrostatic pressure, thus forming a free gas phase. Furthermore, both the sudden and catastrophic, and slow and continuous gas release at surface, of naturally occurring toxic species (CO 2, H 2S and Rn) poses a serious health risk to people living in this geologically active area. This paper presents data obtained from soil gas and gas flux surveys, as well as gas isotopes analyses, which suggest the presence of a deep origin gas flux enriched in carbon dioxide and minor species (CH 4 and H 2S), as well as a channelled migration of geogas mixtures having a Rn component which is not produced in situ. In regards to the health risk to local inhabitants, it was found that some anomalous areas had been zoned as parkland while others had been heavily developed for residential purposes. For example, many new houses were found to have been built on ground which has soil gas CO 2 concentrations of over 70% and a CO 2 flux of about 0.7 kg m −2 day −1, as well as radon values of more than 250 kBq/m 3. In addition, an indoor radon survey has been conducted in selected houses in the town of Cava dei Selci to search for a possible correlation between the local geology and the radon concentration in indoor air. Preliminary results indicate high indoor values at ground floor levels (up to 1000 Bq/m 3) and very high values in the cellars (up to 250.000 Bq/m 3). It is recommended that land-use planners incorporate soil gas and/or gas flux measurements in the environmental assessment of areas of possible risk (i.e. volcanic or structurally active areas).

Large volume phreatomagmatic ignimbrites from the Colli Albani volcano (Middle Pleistocene, Italy)

In this paper we describe four large volume, ash- and accretionary lapilli-rich, phreatomagmatic compound ignimbrite units, mafic in composition, from Colli Albani volcano, south of Rome. The four units, that form the ‘Pisolitic Tuffs’ succession, are separated by paleosols and represent the earliest explosive large volume eruptive episodes from the Quaternary Alban Hills volcano. The occurrence of large volume phreatomagmatic–phreatoplinian eruptions implies the availability of large quantities of water interacting with the rising magma. The paleogeography of the area below the volcano has been reconstructed by the analysis of stratigraphic data from more than a thousand bore-holes distributed around the volcano that allowed to identify NW-trending and NE-trending paleotopographic lows that underlie the central area of the volcano and interpreted as extensional tectonic basins. These lows are filled with Lower to Middle Pleistocene, pre-volcanic lacustrine and fluvial deposits and suggest that at least the central part of the Colli Albani volcanic area hosted a large lake or lagoon. The absence of sedimentary xenoliths in the Pisolitic Tuffs and the low vesicularity of scoria and shards suggest that water interacted with a poorly fragmented magma at very shallow level, triggering the large explosivity of the eruptions. We suggest that water interacting with magma was mostly surficial water related to the presence of the lagoon or lake. In this environment, it is likely that vents were subaqueous allowing a continuous access of water to the conduit. Considering that the minimum calculated volume of products for the Pisolitic Tuffs succession is >37 km 3 and each eruption unit averages approximately around minimum volume of 10 km 3, we suggest that each eruption was related to a caldera collapse, which would have allowed the persistence of a Taupo-like lake in the central area and of phreatoplinian activity. After the last phreatomagmatic eruption, however, the fragmentation style of large volume ignimbrites from Colli Albani became magmatic, suggesting the extinction of the lake after that date. Each of the four units show a basal phreatoplinian fallout level, overlain by a complex association of low aspect ratio surge deposits and ignimbrites. Phreatomagmatic pyroclastic flow deposits are found at distances of more than 40 km from the central area of the volcano, and show important facies variation according to the paleotopography. To the west of the volcano, pyroclastic flows reached the Tyrrhenian coast and emplaced mostly stratified facies on a flat topography, interpreted to reflect both the spreading of pyroclastic flows on an unconfined topography and their interaction with lacustrine and lagoon areas. By contrast, to the east of the volcano, where pyroclastic flows were confined within paleovalleys, the main facies is thick and massive.

Emplacement processes of the mafic Villa Senni Eruption Unit (VSEU) ignimbrite succession, Colli Albani volcano, Italy

The Villa Senni Eruption Unit (VSEU) represents the last large explosive event of the Tuscolano–Artemisio phase of volcanic activity in the Colli Albani (C.A.) (Alban Hills) Volcanic District, situated about 25 km south east of Rome, Italy. The VSEU succession consists of pyroclastic fallout, density current deposits, covering an area of 1500 km 2, reaching a distance of 35 km or more from vent, and having a volume of 30 km 3 DRE. The VSEU is unusual in that its juvenile products are K-foiditic and phono-tephritic in composition, with less than 50% SiO 2 content. The most important products of the VSEU eruption are two pyroclastic density current depositional units; the Tufo Lionato (TL) and Pozzolanelle (TP), with each deposit containing several recognisable internal facies types. A short time gap (hours to days) between the deposition of these two ignimbrites is inferred due to the lack of a palaeosoil or evidence of fluvial reworking at the contact between the two units. A new stratigraphic framework for the VSEU is presented based on field observations, component analyses and detailed lateral correlations, with several new stratigraphic subdivisions proposed. The eruptive sequence is subdivided into depositional facies types, each related to a discrete phase of eruption, and a reconstruction of the three-dimensional geometry and the internal facies association within the VSEU is presented. This reconstruction is used to assess the pyroclastic density current emplacement processes resulting from this ignimbrite forming explosive mafic eruption. The morphology of and internal structures preserved within the mafic VSEU are comparable to those seen in more silicic ignimbrite sequences, suggesting that similar processes of emplacement by pyroclastic density currents can be applied over the entire compositional spectrum. We interpret lateral and vertical facies changes in the VSEU ignimbrite deposits to be caused by changes in the palaeotopographic surface over which the depositing pyroclastic density currents were travelling, as well as spatial and temporal changes in the dynamics of the pyroclastic density currents responsible for their deposition. In particular, interaction between the emplacing pyroclastic density current and the underlying palaeotopography caused local changes in current dynamics, leading to a wide range of localised flow structures and internal facies complexity. These interpretations are made possible because the long axes of valleys into which the VSEU was emplaced, which occur as part of the drainage network surrounding the C.A. volcano, are aligned from 0 to 90° to the radial pyroclastic current direction. The erosive power of pyroclastic density currents is recorded by an erosive contact between the TL and TP ignimbrites in proximal exposures (<12 km) to the north west of the C.A. volcano.

Mineral chemistry and petrogenesis of granular ejecta from the Alban Hills volcano (Central Italy)

A suite of lithics (ejecta) collected from the latest erupted pyroclastic products of the Alban Hills volcano (Central Italy) has been studied to determine their mineralogical composition and to investigate their genesis. The ejecta commonly have granular texture and consist of coarse-grained crystals often associated with a fine- to medium-grained matrix. The mineralogical composition is variable and consists of both typical igneous minerals and contact metamorphic phases. Garnet, clinopyroxene K-feldspar are almost ubiquitous, whereas leucite, wollastonite, sodalite-group minerals, phlogopite, nepheline and phillipsite are present in most of the ejecta; minor and accessory phases include cuspidine, amphibole, pyrrhotite, magnetite, apatite, uranpyrochlore, sphene, kalsilite, and melilite; anorthite, zircon and fluorine-bearing Ca, Zr silicate phases, larnite, and baryte are found sporadically. Ca, REE, Th silicophosphates occur in many samples generally disseminated along interstices and fractures of main minerals. Calcite is present as discrete crystals sometimes enclosed in other minerals, as granules in the fine-grained matrix and as late microcrystalline veins. It shows high oxygen and low carbon isotope ratios with δ18O = + 17.96 to + 27.19, and δ13C = −4.74 to −19.57. Clinopyroxene ranges from diopside to compositions strongly enriched with both Ca-Tschermak’s and esseneite components. Feldspars are generally potassic even though Ba and Sr are found in significant concentrations in some samples. K-feldspars from wollastonite-bearing ejecta are often rimmed with elongated felty crystals identified by X-ray diffraction analysis as leucite. These feldspars show a depletion in Si, and enrichment in Al and K from core to rim. Significant compositional variations are also shown by various other phases such as nepheline, apatite, Ca, REE, Th silicophosphate. The occurrence of igneous and contact metamorphic minerals, as well as the chemical variations of clinopyroxenes and feldspars in the investigated ejecta reveal complex genetic processes related to the interaction between potassic magma and wall rocks. The Ca-rich composition of most phases points to a carbonate nature for the wall rocks. Textural evidence suggests that coarse-grained rocks formed at the margin of the magma chamber were invaded by a late, volatile rich potassic liquid which crystallized as a fine-grained matrix and produced disaggregation and reaction of early formed minerals. Fluid phases percolating through the rocks generated infiltration metasomatism and deposited some uncommon phases rich in Ca, REE, Th, U, which are found along cracks and at the margins of early crystallized minerals. Overall, the all spectrum of the minerals found in this study are also typical of carbonatitic rocks. Their presence in the Alban Hills ejecta demonstrates that their genesis can be related to interaction between ultrapotassic melts and carbonate wall rocks, in addition to precipitation from carbonatitic melts.

Natural Gas Hazard (CO2, 222Rn) within a Quiescent Volcanic Region and Its Relations with Tectonics: The Case of the Ciampino-Marino Area, Alban Hills Volcano, Italy

Groundwater surveys were performed by detailed (around 300 sites) grid-analysis of water temperature, pH, redox potential, electrical conductivity, Rn-222, alkalinity and by calculating the pCO(2), throughout the Ciampino and Marino towns in the Alban Hills quiescent volcano (Central Italy). Following several episodes of dangerous CO2 exhalation from soils during the last 20 years and earlier as historically recorded, the work aimed at assessing the Natural Gas Hazard (NGH) including the indoor-Rn hazard. The NGH was defined as the probability of an area to become a site of poisonous peri-volcanic gas exhalations from soils to the lower atmosphere (comprising buildings). CO2 was found to be a "carrier" for the other poisonous minor and in trace components (H2S, CH4, Rn-222, etc.). This assessment was performed by extrapolating in the aquifer CO2 and Rn-222 conditions, and discriminating sectors where future CO2 flux in soils as well as indoor-Rn measurements have to be noted. A preliminary indoor-Rn survey was performed at about 200 sites. The highest values were found in the highest pCO(2) and high Rn-222 values in groundwater. This indicates convection and enhanced permeability in certain sectors of the main aquifer, i.e., along the bordering faults and inside the gas-trap of the Ciampino Horst., where "continuous gas-phase micro-macro seepage mechanism" is invoked to explain the high peri-volcanic gases flux. Language: en

Strontian fluoro-magnesiohastingsite in Alban Hills lavas (Central Italy): constraints on crystallization conditions

AbstractA magmatic calcic amphibole (M4Ca≥1.50) characterized by large Sr and F contents (SrO&gt;1 wt.%, F&gt;2.5 wt.%) is described. According to the crystal-chemical formula, the amphibole can be classified as a strontian fluoro-magnesiohastingsite and the presence of Sr cations in theAsites is suggested. The amphibole occurs in the groundmass of ultrapotassic lavas from the Alban Hills Volcanic District (Central Italy). This peculiar chemical composition is due to the lavas' groundmass compositional trend occurring under low silica-activity conditions. We suggest that the occurrence of F amphiboles allows us to consider the Alban Hills Volcanic District magmas to be as rich in F as other ultrapotassic magmas.

A large K-foiditic hydromagmatic eruption from the early activity of the Alban Hills Volcanic District, Italy

In this paper we discuss the uncommon case of an energetic, pyroclastic-flow-forming eruption with a SiO2-poor (42–45 wt.%), K-foiditic magma composition. The Trigoria-Tor de' Cenci Tuff (TTC; 561 ka) is the product of the first large-scale explosive event (of the order of 1–10 km3 of erupted products) in the Alban Hills Volcanic District, near the city of Rome, Italy. After an initial Plinian phase that produced a scoria fall horizon, pyroclastic current activity emplaced ash deposits with leucite-bearing juvenile scoria lapilli. The abundance of accretionary lapilli, the most distinctive feature of these deposits, together with the high degree of fragmentation, the abundance of minute lithic inclusions and the morphology of ash particles, indicates a hydromagmatic character for the most part of the eruption. The absence of vent-derived carbonate lithic clasts from the deep regional aquifer and the abundance of cognate lithic fragments suggest that the interaction with external water involved a surficial aquifer in the older Alban Hills volcanic terrains. Perhaps the most striking aspect of the TTC is the K-foiditic composition of the pre-eruptive melt, which, to our knowledge, is unique among explosive events of comparable size elsewhere in the world. The pre-eruptive magma system feeding the TTC was controlled mainly by leucite+clinopyroxene fractionation under aH2O<1 conditions. The low SiO2 activity prevented plagioclase and K-feldspar crystallization. The depth of the magma chamber can be estimated at 3–6 km within the carbonate substrate. In contrast to the other major pyroclastic-flow-forming eruptions of the Alban Hills, the juvenile volatile exsolution due to magma crystallization is not seen as the main mechanism driving the TTC eruption. We suggest that the explosive behaviour of the TTC magma in the early magmatic phase resulted from a rapid decompression due to a regional seismic event and from magma–water interaction in the succeeding phase.

GPS &amp; GLONASS Current Bibliography

his quick bibliography is a compilation of recently (1998 onward) published peer-reviewed articles describing original research with citations that may be of interest to other investigators working in any of the GPS & GLONASS fields. Journal titles are abbreviated following the nomenclature adopted by their respective editors. Titles of new books (•) and conference proceedings (•) that include a significant number of chapters and/or articles dealing with GPS and GLONASS are also listed in this bibliography. Articles, primarily appearing in trade journals, containing interspersed advertisements are only identified by their first page number followed by the symbol +. Contributions with more than five authors will be referenced under the first author name and the extension et al. Acker, Y. et al. 1998. Virgo GPS network: Survey and data processing, Boll. Geod. Sci. Affini, 57(4), 385-404. Al-Gaadi, K.A. and P.D. Ayers. 1998. Assembling real-time DGPS—Testing and investigating factors that affect its accuracy, Applied Engineering in Agriculture, 14(6), 659-665. Anzidei, M. et al. 1998. Utilizzo della rete GPS IGM95 per lo studio delle deformazioni cosismiche dei terremoti umbro-marchigiani del 26 settembre 1997, Boll Geod. Sci. Affini, 57(3), 325-336. Anzidei, M. and A. Galvani. 1999. Monitoring the Alban Hills (Rome, central Italy) volcanic complex by GPS, Boll. Geod. Sci. Affini, 58(1), 1-15. Asher, M.S. 1998. Proposed improvements in precise GPS attitude determination using predetect data, gyro data, and redundant antennas, Advances in the Astronautical Sciences, 100(1), 367-376.

The history of the Monti Sabatini and Alban Hills volcanoes: groundwork for assessing volcanic-tectonic hazards for Rome

The volcanic rocks of Rome provide chronostratigraphic constraint that is of use to geologists, archaeologists, and paleontologists. Identifying the areal distribution of these rocks, their mode of emplacement and a detailed chronology of the eruptive events also, is crucial for assessing local natural hazards in a volcanic-tectonic context, and for recognizing whether the volcanoes may erupt again in the future. We have identified and dated many of the volumetrically significant eruptive units from the Monti Sabatini and Alban Hills (Colli Albani) and propose a formalized volcanic stratigraphy for Rome. It is probable that seismic events triggered some eruptions, as several ignimbrites from the two volcanoes have statistically indistinguishable ages. Following a 200+kyr period of dormancy that was coincident with a pulse of regional uplift, the Alban Hills appears to have begun recently (circa 45ka), a new eruptive cycle. Therefore, accurate assessment of volcanic-tectonic hazards, and estimation of possible future volcanic activity, is necessary for the safety of the five million people living near these volcanoes.

The viability of leucite for 40Ar/ 39Ar dating and as a Quaternary standard

The use of leucite (KAlSi 2O 6) as a 40Ar/ 39Ar dating standard has been avoided largely because of concerns over 40Ar excess. Laser-fusion and resistance furnace step-heating 40Ar/ 39Ar analyses on leucite from a pyroclastic flow deposit from the Alban Hills are concordant and have atmospheric ( 40Ar/ 36Ar=292.1±2.1 and 299.7±2.5, respectively) initial isotopic ratios. The error weighted mean 40Ar/ 39Ar ratio from step-heating and laser fusion data ( N=44) yields an age of 408±2 ka, including propagated errors in standards' isotopic ratios. The step-heating analysis indicates that leucite degasses at quite low temperatures (∼1100°C), making it more suitable for K/Ar age analysis than sanidine. The mean and standard deviation from 10 potassium measurements by flame photometry and the error-weighted mean from five argon extractions produce a K/Ar age of 405±3 ka, in good agreement with the 40Ar/ 39Ar data and with precision comparable to several widely used primary K/Ar standards. This work suggests that leucite could become a very useful primary 40Ar/ 39Ar standard for dating Quaternary age rocks, thereby avoiding errors introduced by intercalibrating a Quaternary-age 40Ar/ 39Ar standard with a primary K/Ar standard.

Pulsed uplift estimated from terrace elevations in the coast of Rome: evidence for a new phase of volcanic activity?

The most recent phase of activity from the Roman volcanoes, since 45 ka, has been interpreted to be the waning stage of the older explosive activity that peaked between 550 and 250 ka. Yet substantial regional uplift from approximately 250 ka suggests that magma chambers beneath the area are growing rather than shrinking. We have estimated the uplift history of the region using radioisotopically and paleomagnetically constrained coastal terrace elevation data that allow us to correlate these terraces with marine oxygen isotopic stages 1–22. Elevations have been corrected for glacio-eustatic sea-level change. Our study shows that over the last million years, regional uplift of coastal terraces occurred in pulses that preceded volcanic activity at roughly 800 ka (in the Monti Sabatini) and 600 ka (in the Alban Hills). The recent pulse of uplift since 250 ka occurred primarily during a period of relative volcanic dormancy that lasted from 250 to 45 ka. We hypothesize that the most recent volcanic activity since 45 ka may reflect the completion of magma chamber recharge, suggesting the start of a new volcanic epoch. It is also possible that the local tectonic stress field changed recently from one dominated by transpression to one dominated by extension, allowing magma to more easily reach the surface via normal faults.

Age of Ancient Monuments by Means of Building Stone Provenance: a Case Study of the Tullianum, Rome, Italy

The construction age of the Tullianum, the oldest portion of the Carcere Mamertino (Mamertine Jail), the early Roman execution site, is not known. Identifying the provenance of the building stone used to construct the Tullianum can aid in determining the approximate age of the structure because the introduction of different types of building materials occurred at known times. The40Ar/39Ar age of the rock used to construct the Tullianum is 36±1ka, indicating that it is Lapis albanus, which crops out only on the flanks of the Alban Hills volcano approximately 20km from Rome. Based on the general belief that the introduction of Lapis albanus as a building stone did not occur before the 4th centurybc , we interpret that the Tullianum was built, or rebuilt, after this time. This age conflicts with the architectural style of the Tullianum, which matches that of ancient cisterns, believed to date to the 7th or 6th centuries bc. This younger age for the Tullianum suggests a unique history for this building, perhaps tied to ancient religious rituals.

Strike-slip faulting and block rotation: a possible triggering mechanism for lava flows in the Alban Hills?

It is suggested in this paper that two distinct tectonic triggers, tapping different depths of a magma reservoir, may be the cause of nearly contemporaneous eruptions of lava flows and ignimbrites in the Alban Hills. The area between the Alban Hills and Rome underwent alternating regional extensional and strike-slip faulting during the Middle Pleistocene. The geometries of the main structural dislocations in Quaternary strata, combined with a statistical analysis of drainage network trends, show a structural pattern that is consistent with local strain partitioning in transpressive zones at strike-slip fault bends, superimposed on regional extension. Based on this analysis, it is suggested that local clockwise block rotation between parallel N–S strike-slip faults might have generated local crustal decompression, allowing relatively volatile-free magma to rise from deep reservoirs beneath the Alban Hills, triggering peripheral fissure lava flows. In contrast, the main ignimbrite eruptions appear to tap shallow, volatile-rich magma reservoirs and are controlled by extensional processes.

U-series disequilibrium study on a gaseous discharge area (Solforata of Pomezia, Alban Hills, Italy): implications for volcanic and geochemical risk

The age and environmental impact of the gaseous discharge at Solforata of Pomezia (Alban Hills, Italy) has been investigated by the application of U-series disequilibrium methods. Chronological data of sulphide mineralization and of a phreatomagmatic deposit close to Solforata fit with a temporal window (26–47 ka BP) of intense volcanic activity which occurred during the final hydromagmatic phase (180–11 ka BP) of the Alban Hills volcano. Radon measurements have allowed an estimation of fluxes of the main gases presently released at Solforata. A model combining Darcy’s law and modified Stoker–Krüger equations has been used in order to predict the upper limit of the gas pressure (19 atmospheres) at the base of the volcanic succession and of the rising time (35 days) of the gas through the volcanic pile. Geochronological and geochemical constraints, obtained by U-series disequilibrium methods, have proved useful in comparing the volcanic and geochemical risks in this area. The comparison shows that, under normal conditions of gas dispersion, the geochemical risk associated with Rn and H 2S exposure is high and it must be tackled immediately with particular surveillance and intervention methods.

F-phlogopites in the Alban Hills Volcanic District (Central Italy): indications regarding the role of volatiles in magmatic crystallisation

A systematic analysis of micas contained in effusive, pyroclastic and hypabyssal rocks of the Alban Hills Volcanic District (AHVD) (Central Italy) was made in order to characterise minerals of pyroclastic units for tephrostratigraphy and to obtain as much information as possible on the activity of volatiles in this magmatic system. The phlogopite shows a large range of F contents (between 0.50 and 7.50 wt%) that make it possible to discriminate different AHVD lithologies; in particular, micas of lava groundmass are characterised by extremely high F (up to 7.50 wt%) and Ba (up to 9.70 wt%) contents, seldom or never found in other magmatic ultrapotassic rocks. Moreover, the micas of pyroclastics, ultramafic cumulates and holocrystalline inclusions made up of leucite, clinopyroxene and phlogopite (hereafter italites) show Mg/(Mg+Fe) values between 0.65 and 0.90 that are not correlated with F contents. The variations in F contents observed in the AHVD micas do not appear to be due to a “temperature” effect or pressure changes, but they may be due to variations in the H 2O and CO 2 activities in the magma chamber. They make it possible to differentiate three crystallisation environments in the AHVD magmatic system. The first one had elevated CO 2 activity and formed the italites near the carbonate contact; these rocks represent, at least those enriched in clinopyroxene without skarn-minerals, the hypabyssal crystallisation of the AHVD magmas at the periphery of magma chamber. The second one, characterised by a higher water activity, is represented by the micas of the ultramafic cumulates and pyroclastic scorias, and is located in the inner part of magma chamber. The third environment, the groundmass of the lavas, it is not related with the previous ones and is characterised by the absence of water and by a high F activity. In general, our results suggest that the compositional variations observed in the micas (Al, Si, Ti, Ba) reflect different H 2O activities (inversely correlated with F activity) in the magma chamber.